Climatic controls on leaf wax hydrogen isotope ratios in terrestrial and marine sediments along a hyperarid-to-humid gradient

The hydrogen isotope composition of leaf wax biomarkers (inline-formulaδ²Hinline-formula_wax) is a valuable tool for reconstructing continental paleohydrology, since it serves as a proxy for the hydrogen isotope composition of precipitation (inline-formulaδ²Hinline-formula_pre). To yield robust palaeohydrological reconstructions using inline-formulaδ²Hinline-formula_wax in marine archives, it is necessary to examine the impacts of regional climate on inline-formulaδ²Hinline-formula_wax and assess the similarity between marine sedimentary inline-formulaδ²Hinline-formula_wax and the source of continental inline-formulaδ²Hinline-formula_wax. Here, we examined an aridity gradient from hyperarid to humid along the Chilean coast. We sampled sediments at the outlets of rivers draining into the Pacific as well as soils within catchments and marine surface sediments adjacent to the outlets of the studied rivers and analyzed the relationship between climatic variables and inline-formulaδ²Hinline-formula_wax values. We found that apparent fractionation between leaf waxes and source water is relatively constant in humid and semiarid regions (average: inline-formula−121 ‰). However, it becomes less negative in hyperarid regions (average: inline-formula−86 ‰) as a result of evapotranspirative processes affecting soil and leaf water inline-formula²H enrichment.

We also observed that along strong aridity gradients, the inline-formula²H enrichment of inline-formulaδ²Hinline-formula_wax follows a non-linear relationship with water content and water flux variables, driven by strong soil evaporation and plant transpiration. Furthermore, our results indicate that inline-formulaδ²Hinline-formula_wax values in marine surface sediments largely reflect inline-formulaδ²Hinline-formula_wax values from the continent, confirming the robustness of marine inline-formulaδ²Hinline-formula_wax records for paleohydrological reconstructions along the Chilean margin. These findings also highlight the importance of considering the effects of hyperaridity in the interpretation of inline-formulaδ²Hinline-formula_wax values and pave the way for more quantitative paleohydrological reconstructions using inline-formulaδ²Hinline-formula_wax.